Sources & Effects of Air Pollution (College Board AP® Environmental Science): Study Guide

What is air pollution?

• Air or atmospheric pollution is the introduction of harmful indoor and outdoor particulates into the air that can negatively affect people's health, environment and climate

  • In the United States, air pollution causes between 90,000 and 360,000 early deaths each year

  • Air pollution in China is estimated to cause between 1.2 and 2.4 million deaths each year

  • The World Health Organization (WHO) estimates that 7 million people die from air pollution each year

• As development occurs in countries around the world, levels of pollution have increased and remains a primary cause of death

Measuring pollution

• Air pollutants are measured as parts per million (ppm)

  • 1 ppm means there is one particle of a pollutant for every 999,999 particles of air

  • The symbol 'm' is one millionth, which is one drop of juice in 40 gallons (150 litres) of water

• Particulate matter particles can be directly emitted (primary particles) or formed in the atmosphere (secondary particles) and are classified by size

  • PM2.5: fine particles with a diameter of 2.5 micrometers or smaller

  • PM10: larger particles with a diameter of 10 micrometers or smaller

Primary & secondary pollutants

• Air pollution involves primary pollutants emitted directly from sources and secondary pollutants formed through chemical reaction

• The combustion of fossil fuels is a major source of primary pollutants

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Controlling air pollution means knowing the formation and effects of primary and secondary pollutants

Primary pollutants

• Primary particles include dust, soot, and sea salt

• Volatile organic compounds (VOCs) are organic chemicals that easily evaporate at room temperature (benzene, formaldehyde, methylene chloride)

  • VOCs contribute to the formation of ground-level ozone and smog

• Ammonia (NH₃) is a colorless, highly irritating and corrosive gas with a sharp, choking odor

  • It dissolves easily in water to form ammonium hydroxide (NH₄OH) solution, which can cause irritation and burns

  • Ammonia gas is formed from organic matter breakdown and fertilizers

  • It is a primary pollutant that contributes to secondary particulate matter (PM) when it interacts with other atmospheric gases

• Black carbon or soot, is fine particulate matter emitted from incomplete combustion, contributing to air pollution and climate change

• Oxides of carbon (CO_x):

  • carbon monoxide (CO) is a colourless, odourless gas that is harmful to human health and can lead to carbon monoxide poisoning

  • carbon dioxide (CO₂) is a greenhouse gas responsible for global warming and climate change

• Oxides of nitrogen (NO_x):

  • nitrogen dioxide (NO₂) and nitrogen oxide (NO) are key contributors to air pollution, causing respiratory issues and contributing to the formation of smog

• Oxides of sulfur (SO_x): sulfur dioxide (SO₂) and sulfur trioxide (SO₃) are released during fossil fuel combustion, leading to acid rain and respiratory problems

Secondary pollutants

• Secondary pollutants form in the atmosphere through the chemical reactions of primary pollutants

• Secondary particles form through chemical reactions (sulfates, nitrates, organic compounds)

• Tropospheric ozone (O₃) is formed through a complex series of reactions

  • Primary pollutant nitrogen dioxide (NO₂) releases oxygen atoms (O) in the presence of sunlight that react with oxygen molecules (O₂) already in the atmosphere to form secondary pollutant ozone (O₃)

  • Tropospheric ozone is a harmful air pollutant that causes respiratory problems and contributes to smog

• Nitrogen oxides (NO_x) contribute to the formation of secondary pollutants such as nitric acid (HNO₃) and nitrate particles, which contribute to acid rain and particulate matter pollution

Criteria air pollutants

• Criteria air pollutants are six harmful substances in the air that can lead to smog, acid rain, and health issues

• These are:

  • nitrogen dioxide (NO₂)

  • sulfur dioxide (SO₂)

  • carbon monoxide (CO)

  • particulate matter (PM)

  • ozone (O₃)

  • lead (Pb)

• They come from various sources like factories, mining, transportation, energy production, and farming

• They were the first pollutants identified by the U.S. Environmental Protection Agency (EPA) that required national guidelines

• Most of these pollutants come from burning fossil fuels or industrial activities

Burning coal

• Burning coal releases harmful substances like small particles, fly ash, and heavy metals like mercury and lead, along with carbon dioxide, sulfur dioxide, and nitrogen oxide

• Coal power plants are among the most polluting energy sources

Impacts of burning coal

• Health effects: exposure to these pollutants can cause breathing problems like asthma and lung disease and can also raise the chance of heart issues, especially from fine (PM2.5) particles in the air

• Acid rain: when mixed with water vapor in the atmosphere, sulfur dioxide emitted from coal combustion contributes to acid rain formation

• Smog is formed when nitrogen oxides from burning coal mix with sunshine

  • This is particularly evident in places that get a lot of sun, such as Los Angeles

• Burning coal contributes to climate change through the release of carbon dioxide

Burning fossil fuels

• Fossil fuel combustion produces a mix of pollutants, including:

  • carbon monoxide, especially from incomplete combustion

  • nitrogen oxide from vehicle engines and power plants

  • sulfur dioxides, mainly from burning coal

  • hydrocarbons, typically coming from sources like petroleum (oil), natural gas, and their byproducts

  • particulates such as soot and fine particles

• The combustion of fossil fuels releases nitrogen oxides into the atmosphere

  • This leads to the production of ozone, the formation of photochemical smog, and the conversion to nitric acid in the atmosphere, causing acid rain

• Other sources of air pollution include factories, volcanoes, and campfires, which release many of the same gases and particles as coal and fossil fuels

Releasing sulfur dioxide

• Air quality can be affected through the release of sulfur dioxide during the burning of fossil fuels, mainly diesel fuels

• Sulfur dioxide (SO₂) is a significant contributor to acid rain and respiratory problems due to its irritating effects on the lungs when inhaled at high concentrations

• Mainly released by coal-burning power plants and factories and also from activities like metal mining

• Acid rain: when sulfur dioxide mixes with water vapor in the air, it creates sulfuric acid, which is an important part of acid rain

  • Acid rain can harm forests, aquatic environments, and historical buildings

• Health effects: breathing in sulfur dioxide can damage the airways, worsen asthma, cause coughing, and lead to breathing problems, especially for people who are more vulnerable

Managing lead

• Lead (Pb) is a toxic metal that can be emitted from:

  • industrial processes, like mining, lead smelting, battery manufacturing, metal processing facilities, and waste incineration

  • products such as lead-based paint and leaded gasoline

• Health effects: inhaling lead is very harmful, especially for young children

  • It can damage the brain, nervous system, and growth

• Lead is toxic, so environmental agencies worldwide carefully control lead pollution, leading to a drop in lead levels in the air, particularly when leaded gasoline was banned globally

  • The Environmental Protection Agency (EPA) and the Clean Air Act regulate the use of lead in the US, particularly in fuels, which dramatically decreased the amount of lead in the atmosphere